1. Field of the Invention
The present invention relates to an exchange coupling film which has an antiferromagnetic layer and a ferromagnetic layer, wherein the direction of magnetization of the ferromagnetic layer is fixed in a predetermined direction by the effect of an exchange magnetic field which is generated at the interface between the antiferromagnetic layer and the ferromagnetic layer. More particularly, the present invention relates to an exchange coupling film which is improved to exhibit a large ratio of resistance variation and also to a magnetoresistive sensor, e.g., a spin valve thin-film device or an ARM device, incorporating such an exchange coupling film, as well as to a thin-film magnetic head which uses such a magnetoresistive sensor.
2. Description of the Related Art
A spin-valve-type thin-film device is a kind of GMR (Giant Magnetoresistive) device which makes use of a giant magnetoresistive effect, and is used for detecting recording magnetic fields from a recording medium such as a hard disk.
The spin-valve-type thin-film device, among various GMR devices, has advantageous features such as simplicity of the structure and high subtlety to vary its magnetic resistance even under a weak magnetic field.
The simplest form of the spin-valve-type thin-film device has an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic intermediate layer, and a free magnetic layer. The antiferromagnetic layer and the pinned magnetic layer are formed in contact with each other, and the direction of the pinned magnetic layer is put into a single magnetic domain state and fixed by an exchange anisotropic magnetic field, which is produced at the interface between the antiferromagnetic layer and the pinned magnetic layer. The magnetization of the free magnetic layer is aligned in a direction which intersects the direction of magnetization of the pinned magnetic layer, by the effect of bias layers that are formed on both sides of the free magnetic layer.
Alloy films such as an Fexe2x80x94Mn (Iron-Manganese) alloy film, Nixe2x80x94Mn (Nickel-Manganese) alloy film and a Ptxe2x80x94Mn (Platinum-Manganese) alloy film are generally usable as the material of the antiferromagnetic layer, among which the Ptxe2x80x94Mn alloy film are attracting attention due to its advantages such as a high blocking temperature, superior corrosion resistance, and so forth.
In order to comply with the future demand for higher recording density, it is important to achieve greater exchange coupling magnetic field and greater ratio of resistance variation. However, it has been impossible to obtain a large ratio of resistance variation, with the conventional structure of the magnetoresistive sensor which is composed of an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic intermediate layer and a free magnetic layer.
It has been recognized that the ratio of resistance variation has dependency on exchange coupling magnetic field: the resistance variation ratio decreases unless a large exchange coupling magnetic field is obtained. The resistance variation ratio also has dependency on the crystalline orientations of the layers. With the conventional structure, it has been impossible to obtain a magnetoresistive sensor that possesses both appropriate crystalline orientations and a large exchange magnetic field, and that accordingly exhibits a large resistance variation ratio.
The present invention is aimed at overcoming these problems, by providing an exchange coupling film having an antiferromagnetic layer, a ferromagnetic layer, and a seed layer formed on the side of the antiferromagnetic layer opposite to the interface between the antiferromagnetic layer and the ferromagnetic layer. The seed layer serves to optimize the crystalline orientations of the layers so as to provide a large ratio of resistance variation. The present invention also provides a magnetoresistive sensor using this exchange coupling film and also a thin-film magnetic head using such a magnetoresistive sensor.
In accordance with a first aspect of the present invention, there is provided an exchange coupling film comprising: an antiferromagnetic layer; a ferromagnetic layer arranged such that an exchange coupling magnetic field is produced at the interface between the antiferromagnetic layer and the ferromagnetic layer; and a seed layer formed on the side of the antiferromagnetic layer opposite to the ferromagnetic layer, the seed layer having face-centered cubic crystals with the (111) plane substantially oriented in parallel with the interface; wherein the crystalline structure of at least part of the antiferromagnetic layer comprises CuAuxe2x80x94I type face-centered ordered lattice, wherein the antiferromagnetic layer and the ferromagnetic layer have crystalline orientations in which the (111) planes are oriented in parallel with the interface, and wherein a non-aligned crystal lattice state is created at at least part of the interface between the antiferromagnetic layer and the seed layer.
The structure of the exchange coupling film of the present invention has been subjected to a heat treatment after the deposition of the layers constituting the exchange film.
The exchange coupling film of the present invention has the seed layer formed on the side of the antiferromagnetic layer opposite to the interface between the antiferromagnetic layer and the ferromagnetic layer. The seed layer has a crystalline structure composed mainly by face-centered cubic crystals having the (111) planes substantially oriented in parallel with the above-mentioned interface. The seed layer thus formed serves to cause the (111) planes of the antiferromagnetic layer and the ferromagnetic layer to be in parallel with the interface therebetween, thus offering remarkable improvement in the ratio of resistance variation of a magnetoresistive sensor incorporating the exchange coupling film.
In order to obtain a large exchange coupling magnetic field at the interface between the antiferromagnetic layer and the ferromagnetic layer, a non-aligned state has been created at at least part of the interface between the antiferromagnetic layer and the seed layer. This means that transformation from disordered lattice to ordered lattice has been properly effected, and indicates that an exchange coupling film is obtainable that has a large exchange coupling magnetic field. The ratio of resistance variation has dependency also on the strength of the exchange coupling magnetic field, so that the ratio of resistance variation can be increased as a result of the increase of the exchange coupling.
In accordance with a second aspect of the present invention, there is provided an exchange coupling film comprising: an antiferromagnetic layer; a ferromagnetic layer arranged such that an exchange coupling magnetic field is produced at the interface between the antiferromagnetic layer and the ferromagnetic layer; and a seed layer formed on the side of the antiferromagnetic layer opposite to the ferromagnetic layer, the seed layer having face-centered cubic crystals with the (111) plane substantially oriented in parallel with the interface; wherein the crystalline structure of at least part of the antiferromagnetic layer comprises CuAuxe2x80x94I type face-centered ordered lattice, wherein the antiferromagnetic layer and the ferromagnetic layer have crystalline orientations in which the (111) planes are oriented in parallel with the interface, and wherein the antiferromagnetic layer and the seed layer have different lattice constants at the interface therebetween.
Unlike the first aspect described before, the second aspect features that the antiferromagnetic layer and the seed layer have different lattice constants at the interface therebetween. Preferably, a crystal lattice non-aligned state is created at at least part of the interface between the antiferromagnetic layer and the seed layer.
In accordance with this aspect of the present invention, the antiferromagnetic layer may be made from an antiferromagnetic alloy material containing an element X and Mn, wherein the element X is selected from the group of elements consisting of Pt, Pd, Ir, Rh, Ru, and Os and combinations thereof, or from an antiferromagnetic alloy material containing an element X, an element Xxe2x80x2 and Mn, where the element Xxe2x80x2 is selected from the group of elements consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb and a rare earth element and combinations thereof.
Preferably, the antiferromagnetic alloy material containing an element X, an element Xxe2x80x2 and Mn is an interstitial solid solution in which the element Xxe2x80x2 has invaded and resides in the interstices of a space lattice constituted by the element X and Mn, or a substitutive solid solution in which part of the lattice points of a crystal lattice constituted by the element X and Mn has been substituted by the element Xxe2x80x2.
This permits the Xxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy to have a large lattice constant, while enhancing the difference in the lattice constant between the ferromagnetic layer and the antiferromagnetic layer, thus facilitating the creation of the non-aligned crystal lattice state at the interface between the ferromagnetic layer and the antiferromagnetic layer.
In accordance with a third aspect of the present invention, there is provided an exchange coupling film comprising: an antiferromagnetic layer made from an antiferromagnetic alloy material containing an element X and Mn, wherein the element X is selected from the group of elements consisting of Pt, Pd, Ir, Rh, Ru, and Os and combinations thereof; a ferromagnetic layer arranged such that an exchange coupling magnetic field is generated at the interface between the antiferromagnetic layer and the ferromagnetic layer; and a seed layer formed on the antiferromagnetic layer at the side of the antiferromagnetic layer opposite to the interface, and having (111) planes of face-centered cubic crystals substantially oriented in parallel with the interface; wherein the antiferromagnetic layer has a region in which the ratio of atomic percent of the element X to Mn increases in a direction towards the seed layer, wherein the crystalline structure of at least part of the antiferromagnetic layer has a CuAuxe2x80x94I face-centered cubic ordered lattice, and wherein the antiferromagnetic layer and the ferromagnetic layer have such crystal orientations that the (111) planes are substantially oriented in parallel with the interface between the antiferromagnetic layer and the ferromagnetic layer.
Alternatively, this aspect of the present invention provides an exchange coupling film comprising: an antiferromagnetic layer made from an antiferromagnetic alloy material containing an element X, an element Xxe2x80x2 and Mn, wherein the element X is selected from the group of elements consisting of Pt, Pd, Ir, Rh, Ru, and Os and combinations thereof, while the element Xxe2x80x2 is selected from the group of elements consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb and a rare earth element and combinations thereof; a ferromagnetic layer arranged such that an exchange coupling magnetic field is generated at the interface between the antiferromagnetic layer and the ferromagnetic layer; and a seed layer formed on the antiferromagnetic layer at the side of the antiferromagnetic layer opposite to the interface, and having (111) planes of face-centered cubic crystals substantially oriented in parallel with the interface, wherein the antiferromagnetic layer has a region in which the ratio of atomic percent of the element X to Mn increases in a direction towards the seed layer, wherein the crystalline structure of at least part of the antiferromagnetic layer has a CuAuxe2x80x94I face-centered cubic ordered lattice, and wherein the antiferromagnetic layer and the ferromagnetic layer have such crystal orientations that the (111) planes are substantially oriented in parallel with the interface between the antiferromagnetic layer and the ferromagnetic layer.
Preferably, the antiferromagnetic alloy material containing an element X, an element Xxe2x80x2 and Mn is an interstitial solid solution in which the element Xxe2x80x2 has invaded and resides in the interstices of a space lattice constituted by the element X and Mn, or a substitutive solid solution in which part of the lattice points of a crystal lattice constituted by the element X and Mn has been substituted by the element Xxe2x80x2. The antiferromagnetic layer and the seed layer may have different lattice constants at the interface therebetween. Preferably, a non-aligned crystal lattice state has been created at at least part of the interface between the antiferromagnetic layer and the seed layer.
The presence of the region in which the ratio of the atomic percent of the element X or the elements X+Xxe2x80x2 to Mn increases in a direction towards the seed layer frees the antiferromagnetic layer from the restraint effected by the crystalline structure of the seed layer at the interface between the antiferromagnetic layer and the seed layer, whereby the antiferromagnetic layer is properly transformed into ordered structure to offer a greater exchange magnetic field than those obtainable with known devices.
The structure may be such that, assuming a first imaginary boundary at the side of the thicknesswise center of the antiferromagnetic layer adjacent to the seed layer and a second imaginary boundary at the side of the thicknesswise center adjacent to the ferromagnetic layer, the ratio is greater in the region between the interface adjacent to the seed layer and the first imaginary boundary than in the region between the first and second imaginary boundaries, and the ratio linearly or non-linearly increases towards aid interface adjacent to the seed layer in a region which includes the first imaginary boundary.
Preferably, the antiferromagnetic layer has a region in which the atomic percent of the element X or the elements X+Xxe2x80x2 increases in a direction towards the seed layer starting from a thicknesswise location within the antiferromagnetic layer. This feature provides a greater exchange coupling magnetic field.
It is also preferred that the antiferromagnetic layer has a region which is near the interface between the antiferromagnetic layer and the seed layer and in which the atomic percent of the element X or the elements X+Xxe2x80x2 decreases in a direction towards the seed layer. This feature also provides a greater exchange coupling magnetic field.
It is also preferred that the composition ratio of the element X or the elements X+Xxe2x80x2 of the antiferromagnetic layer to the total composition ratio 100 at % of all the elements constituting the antiferromagnetic layer is about preferably about 50 at % to about 65 at % and, more preferably about 50 at % to about 60 at %, in the region near the interface between the antiferromagnetic layer and the seed layer.
Preferably, a region exists near the thicknesswise center of the antiferromagnetic layer, the region having a composition ratio of the element X or the elements X+Xxe2x80x2 about of preferably about 44 at % to about 57 at % and, more preferably about 46 wt % to about 55 at % of said element X where a total composition ratio of all the elements is expressed as 100 at %. This means that transformation from disordered lattice to ordered lattice has been properly performed, thus suggesting that a large resistance variation ratio and large exchange coupling magnetic field are obtainable.
Preferably, the antiferromagnetic layer has a thickness at least about 76 xc3x85. Thus, the present invention offers greater resistance variation ratio and greater exchange coupling magnetic field than ever, even with such a small thickness of the antiferromagnetic layer.
It is also preferred that the seed layer is formed of an Nixe2x80x94Fe alloy or an Nixe2x80x94Fexe2x80x94Y alloy, wherein Y is one or more elements selected from the group consisting of Cr, Rh, Ta, Hf, Nb, Zr, and Ti. In particular, the seed layer is a non-magnetic layer. This serves to suppress shunting of the sense current to the seed layer, thus contributing to the improvement in the resistance variation ratio.
It is also preferred that the seed layer, the antiferromagnetic layer, and the ferromagnetic layer are sequentially formed in this order on an underlying layer, the underlying layer being formed of at least one element selected from the group consisting of Ta, Hf, Nb, Zr, Ti, Mo and W. This feature enables the seed layer formed on the underlying layer to have a crystalline structure composed mainly of face-centered cubic crystals, with the (111) plane substantially oriented in parallel with the aforementioned interface.
Preferably, the antiferromagnetic layer and the ferromagnetic layer have different lattice constants at at least part of the interface therebetween. In particular, it is preferred that a non-aligned crystal lattice state has been created at at least part of the interface between the antiferromagnetic layer and the ferromagnetic layer. The presence of such a non-aligned crystal lattice state at the interface between the ferromagnetic layer and the antiferromagnetic layer enables appropriate transformation in the whole antiferromagnetic layer, thus ensuring a large exchange coupling magnetic field.
The exchange coupling film having the described features can be used in a variety of types of magnetoresistive sensors.
Thus, in accordance with a different aspect of the present invention, there is provided a magnetoresistive sensor, comprising: an antiferromagnetic layer; a pinned magnetic layer which is formed in contact with the antiferromagnetic layer and having a direction of magnetization fixed by an exchange anisotropic magnetic field with the antiferromagnetic layer; a non-magnetic intermediate layer formed between the pinned magnetic layer and a free magnetic layer; and a bias layer for aligning the direction of magnetization of the free magnetic layer in a direction which intersects the direction of magnetization of the pinned magnetic layer; wherein the antiferromagnetic layer and the pinned magnetic layer formed in contact with the antiferromagnetic layer are formed of the exchange coupling film described before, and wherein the nonmagnetic intermediate layer and the free magnetic layer have crystalline orientations with the (111) planes substantially oriented in parallel with the interface between the antiferromagnetic layer and the pinned magnetic layer. Thus, the layers from the antiferromagnetic layers to the free magnetic layer, inclusive of other layers therebetween, have crystalline orientations with the (111) planes substantially oriented, whereby a large resistance variation ratio is obtainable.
A magnetoresistive sensor, comprising: an antiferromagnetic layer; a pinned magnetic layer which is formed in contact with the antiferromagnetic layer and having a direction of magnetization fixed by an exchange anisotropic magnetic field with the antiferromagnetic layer; a non-magnetic intermediate layer formed between the pinned magnetic layer and a free magnetic layer; and an antiferromagnetic exchange bias layer formed on either the upper side or the lower side of the free magnetic layer and having portions spaced from each other in the track width direction; wherein the exchange bias layer and the free layer are formed of the exchange coupling film described before, and wherein the nonmagnetic intermediate layer, the pinned magnetic layer and the antiferromagnetic layer have crystalline orientations with the (111) planes substantially oriented in parallel with the interface between the exchange bias layer and the free magnetic layer.
The substantial orientations of the (111) planes in the layers from the antiferromagnetic layer to the free magnetic layer provides a greater resistance variation ratio than those obtainable with known devices.
In accordance with the present invention, there is provided a magnetoresistive sensor comprising: a free magnetic layer; non-magnetic intermediate layers formed on upper and lower sides of the free magnetic layer; pinned magnetic layers one of which is formed on the upper side of one of the non-magnetic intermediate layers while the other on the lower side of the other of the non-magnetic intermediate layers; antiferromagnetic layers one of which is formed on the upper side of the one of the pinned magnetic layers while the other on the lower side of the other of the pinned magnetic layers, the antiferromagnetic layers serving to fix the directions of magnetization of the associated pinned magnetic layers by exchange anisotropic magnetic fields; and a bias layer which aligns the direction of magnetization of the free magnetic layer to a direction that intersects the directions of the pinned magnetic layers; wherein the antiferromagnetic layer and the pinned magnetic layer contacting therewith, at least one of the upper and lower sides of the free magnetic layer, are formed of the exchange coupling film described before, and wherein the layers other than the exchange coupling film have crystalline orientations with the (111) planes substantially aligned in parallel with the interface between the antiferromagnetic layer and the pinned layer. Thus, the laminate of the layers starting from one of the pinned magnetic layer and terminating in the other pinned magnetic layer have crystalline orientations with the (111) planes substantially oriented, whereby the magnetoresistive sensor exhibits a greater ratio of resistance variation than those obtainable with known devices.
The present invention also provides a magnetoresistive sensor comprising: a non-magnetic layer; a magnetoresistive layer and a soft magnetic layer and the non-magnetic layer therebetween; and an antiferromagnetic layer formed on the upper side or the lower side of the magnetoresistive layer and having portions spaced from each other in the track width direction; wherein the antiferromagnetic layer and the magnetoresistive layer and the magnetoresistive layer are formed of the exchange coupling film described before, and wherein the non-magnetic layer and the soft magnetic layer have crystalline orientations with the (111) planes substantially oriented in parallel with the interface between the magnetoresistive layer and the antiferromagnetic layer. Thus, the magnetoresistive layer and the soft magnetic layer, as well as intervening layer, have crystalline orientations with the (111) planes substantially oriented, whereby the magnetoresistive sensor exhibits a greater ratio of resistance variation than those obtainable with known devices.
The present invention also provides a magnetoresistive sensor having shield layers provided on the upper and lower sides of the above-mentioned magnetoresistive sensor through the intermediaries of gap layers.